Arrangement for scattering electrons

Abstract

An arrangement is provided for scattering electrons in an electron accelerator capable of variable acceleration energies. The arrangement has two scattering foils arranged at a mutual spacing from one another along a direction of an electron beam. A first scattering foil in the beam direction has a constant thickness whereas a second scattering foil has a thickness which decreases from its center towards its margin. The first scattering foil comprises a set of foils each of which have a scattering capability which corresponds to a selectable acceleration energy. The appropriate member of the set is selected and placed in the beam as the first scattering foil so as to create a relatively constant intensity of radiation over a given volume. The second scattering foil, which is of a more costly and complex construction, remains unchanged in the electron beam.

Claimed as my invention: 
     
       1. An arrangement for scattering electrons in an electron accelerator with selectable acceleration energies, comprising: (a) acceleration means for providing a beam of electrons;   (b) first and second scattering foils arranged at a mutual spacing from one another along a direction of the beam for producing scattering properties;   (c) the first scattering foil in the beam direction having a constant thickness;   (d) the second scattering foil having a thickness decreasing from its center towards its margin;   (e) means for adapting the scattering properties to the selected acceleration energy including a set of scattering foils, each having a scattering property corresponding to a selected acceleration energy, the scattering properties of the set of foils decreasing with decreasing acceleration energy, a corresponding one of said set of foils being placed by said means into the beam path of said first scattering foil for a second acceleration energy; and   (f) said second scattering foil remaining unchanged in the beam.   
     
     
       2. An arrangement in accordance with claim 1, characterized in that the second scattering foil comprises several concentrically and rigidly superimposed circular disc-shaped foils of different diameters and thicknesses. 
     
     
       3. An arrangement in accordance with claim 2, characterized in that the margins of said disc-shaped foils are inclined. 
     
     
       4. An arrangement in accordance with claim 2, characterized in that the disc-shaped foils forming the second scattering foil are mounted between two carrier foils made of an organic material, said carrier foils being mounted between clamping rings. 
     
     
       5. An arrangement in accordance with claim 4 in which said organic material comprises polystyrol. 
     
     
       6. An arrangement in accordance with claim 1, characterized in that the first scattering foil is comprised of a material of high atomic number. 
     
     
       7. The arrangement of claim 6 in which said material of high atomic number consists of lead. 
     
     
       8. An arrangement in accordance with claim 1, characterized in that the second scattering foil is comprised of a material of a low atomic number. 
     
     
       9. The arrangement of claim 8 in which said material of low atomic number consists of aluminum. 
     
     
       10. An arrangement for scattering electrons in an electron accelerator with selectable acceleration energies, comprising: (a) acceleration means for providing a beam of electrons;   (b) first and second scattering foils arranged at a mutual spacing from one another along a direction of the beam for scattering the electron beam to produce a relatively constant intensity of the beam over a given volume;   (c) the first scattering foil in the beam direction having a relatively constant thickness;   (d) the second scattering foil in the beam direction having a variable thickness;   (e) said first scattering foil comprising one of a set of foils, each foil in the set having a differing scattering property which corresponds to a selected acceleration energy, the scattering properties of the set decreasing with decreasing acceleration energy; and   (f) means for selecting a corresponding one of said set of foils and placing it in the beam in accordance with a selected acceleration energy.   
     
     
       11. The arrangement of claim 10 in which said means for selecting comprises a carrier with a sled movable thereover, said sled having mounted thereon the set of foils and being motor driven.